Backlight unit and display apparatus including the same

ABSTRACT

A backlight unit and a display apparatus including the backlight unit are provided. The backlight unit includes: a light source unit which includes at least one light source which emits light, and a gap maintaining unit; a light guiding plate which guides the light emitted from the light source; and an elastic member which elastically biases the light source unit toward the light guiding plate so that the gap maintaining unit maintains a gap between the light source and the light guiding plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Korean Patent Application No.10-2008-0118642, filed on Nov. 27, 2008, and Korean Patent ApplicationNo. 10-2009-0100591 filed on Oct. 22, 2009, the disclosures of which areincorporated herein by reference.

BACKGROUND

1. Field

Apparatuses consistent with the exemplary embodiments relate to abacklight unit and a display apparatus including the same, and moreparticularly, to a backlight unit which provides necessary light bymaintaining a gap between a light source unit and a light guiding plateregardless of expansion or contraction of the light guiding plate due toheat, and a display apparatus including the same.

2. Description of the Related Art

Backlight units may be classified as a direct type backlight unit and anedge type backlight unit depending on a location of a light source.

The direct type backlight unit has a light source disposed below aliquid crystal panel so that the light source emits light directly tothe liquid crystal panel. The direct type backlight unit includes areflection plate which is located under a lamp to reflect light, and anoptical sheet which is disposed above the lamp to focus and diffuse theemitted light. As the direct type backlight unit may include a pluralityof light sources and provide high efficiency in using light, it ismainly employed in a large-screen liquid crystal display (LCD) devicethat requires high brightness.

An edge type backlight unit typically has a light guiding plate disposedat a lateral side of a light source to guide light from a light sourceto a liquid crystal panel. The edge type backlight unit has a lowerbrightness when employed in a large-screen liquid crystal displaydevice, but is advantageous in a thin display device. The light guidingplate diffuses light to make it uniform. Below the light guiding plateis provided a reflection plate. Above the light guiding plate, a pair ofprism sheets which convert a path of light, and a diffusion sheet whichreinforces uniformity of light incident to the liquid crystal panel areformed.

Generally, the light guiding plate includes polymer methyl methacrylate(PMMA). The PMMA expands and contracts in reaction to changes intemperature and moisture, and has a large expansion coefficient amongother plastic materials.

In case of a large backlight unit, a light emitting diode (LED) employedas a light source should be as close to the light guiding plate aspossible to provide sufficient light. The greater the gap between theLED and the light guiding plate is, the lower light efficiency is. If anLED is employed in an edge type backlight unit have a size greater than40 inches, the size of the light guiding plate also increases. Thus,changes in the size of the light guiding plate (i.e., expanding orcontracting) due to heat or moisture increases. If the LED is closelyprovided to the light guiding plate for light efficiency, the lightguiding plate expands in a high-temperature operation environment andcontacts the LED. On the contrary, if the gap between the LED and thelight guiding plate increases to solve the foregoing issue, it isdifficult to provide necessary light.

SUMMARY

One or more exemplary embodiments provide a backlight unit capable ofmaintaining the brightness of a light source irrespective of deformationof a light guiding plate, and a display apparatus including the same.

According to an aspect of an exemplary embodiment, there is provided abacklight unit including: a light source unit which includes at leastone light source which emits light, and a gap maintaining unit; a lightguiding plate which guides the light emitted from the light source; andan elastic member which elastically biases the light source unit towardthe light guiding plate so that the gap maintaining unit maintains aconstant gap between the light source and the light guiding plate

The light source unit may further include a point light source and apoint light source substrate on which the point light source isdisposed, wherein the gap maintaining unit extends from the point lightsource substrate to the light guiding plate.

The gap maintaining unit may be integrally formed with the point lightsource substrate.

A section of the point light source substrate and the gap maintainingunit may have at least one of a U-shape, an L-shape and a ├-shape.

The backlight unit may further include an accommodation member whichaccommodates the light source unit and the light guiding plate, whereinthe elastic member is coupled to and disposed between the accommodationmember and the light source unit.

The elastic member may further include at least one of a coil spring, arubber, a graphite tape, a graphite sheet and a sponge.

The light source may be arranged along a lateral side of the lightguiding plate.

The light source may comprise a light emitting diode.

According to aspect of another exemplary embodiment, there is provided adisplay apparatus including: a video receiver which receives a videosignal; a signal processor which processes the received video signal; adisplay panel which displays an image based on the processed videosignal; and a backlight unit which provides light to the display panel,the backlight unit including: a light source unit which includes atleast one light source which emits light, and a gap maintaining unit; alight guiding plate which guides the light emitted from the lightsource; and an elastic member which elastically biases the light sourceunit toward the light guiding plate so that the gap maintaining unitmaintains a gap between the light source and the light guiding plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become apparent and more readilyappreciated from the following description of the exemplary embodiments,taken in conjunction with the accompanying drawings of which:

FIGS. 1A and 1B are sectional views which illustrate contraction of anelastic member depending on deformation of a light guiding plate of abacklight unit according to an exemplary embodiment;

FIG. 2 is a detail view of A in FIG. 1A;

FIG. 3 is a sectional view of a related art backlight unit;

FIG. 4 is a perspective view of a display apparatus according to anexemplary embodiment;

FIG. 5 is a control block diagram of a display apparatus of FIG. 4;

FIG. 6 is a sectional view of a backlight unit according to anotherexemplary embodiment;

FIG. 7 is a sectional view of a backlight unit according to stillanother exemplary embodiment; and

FIG. 8 shows a light source included in the backlight unit according toan exemplary embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments will be described with reference toaccompanying drawings, wherein like numerals refer to like elements andrepetitive descriptions will be avoided as necessary.

FIGS. 1A and 1B are sectional views of a backlight unit according to anexemplary embodiment, and illustrate contraction of an elastic memberdepending on deformation of a light guiding plate.

As shown therein, a backlight unit according to the present exemplaryembodiment includes a light source unit 110, a light guiding plate 120,an optical sheet 130 provided above the light guiding plate 120, areflection plate 140 provided below the light guiding plate 120 and anaccommodation member 150 accommodating the foregoing elements. Thebacklight unit further includes an elastic member 160 which is providedbetween the accommodation member 150 and the light source unit 110. Thebacklight unit according to the present exemplary embodiment is an edgetype where the light source unit 110 is provided in a row in a specificdirection.

The light guiding plate 120 is provided in a lateral side of the lightsource unit 110 to receive light from the light source unit 110. Thelight guiding plate 120 includes acrylic resin such as PMMA, anduniformly supplies light from the light source unit 110 to the opticalsheet 130. The light guiding plate 120 has a rectangular shape, but notlimited thereto. Alternatively, the light guiding plate 120 may havevarious shapes depending on the shape of a panel receiving light.

The optical sheet 130 may include a diffusion panel, a prism film, aprotection film, etc. which are not shown. The optical sheet 130uniformly diffuses light emitted by the light guiding plate 120.

The reflection plate 140 reflects light incident on a lower part of thelight guiding plate 120 back to the optical sheet 130 to be supplied tothe light guiding plate 120. The reflection plate 140 may include polyethylene terephthalate (PET) or poly carbonate (PC) coated with silveror aluminum.

FIG. 2 is an enlarged view of A in FIG. 1A, and specifies the lightsource unit 110 and the elastic member 160. As shown therein, the lightsource unit 110 includes a point light source 111 as a light source, apoint light source substrate 112 on which the point light source 111 isdisposed, and gap maintaining units 113 and 114 extending from the pointlight source substrate 112. The elastic member 160 is coupled with thelight source unit 110 from a lateral side of the light source unit 110.

The point light source 111 is disposed on the point light sourcesubstrate 112 shaped like a bar, and includes a plurality of LEDs. Thetemperature of the point light source 111 may rise to tens of degreesdue to light emission. The plurality of LEDs emitting light in differentcolors may form a group as the point light source 111 and may beprovided as an LED emitting white light. The point light source 111 mayinclude a laser diode, etc. other than the LED.

The point light source substrate 112 may include a circuit substratehaving a circuit pattern supplying power to the point light source 111,and may include aluminum, which is highly conductive.

The gap maintaining units 113 and 114 extend from the point light sourcesubstrate 112 to the light guiding plate 120, and maintain a gap G1between the light guiding plate 120 and the point light source 111. Asshown therein, the gap maintaining units 113 and 114 according to thepresent exemplary embodiment accommodate the point light source 111together with the point light source substrate 112, and have a U-shaped(

-shaped) section open in a direction of the light guiding plate 120. Thegap maintaining units 113 and 114 may be provided integrally with thepoint light source substrate 112. Alternatively, the point light sourcesubstrate 112 and the gap maintaining units 113 and 114 may be coupledto each other.

An end part of the gap maintaining units 113 and 114 extending from thepoint light source substrate 112 contacts a surface of the light guidingplate 120, and the gap G1 is maintained between the point light source111 and the light guiding plate 120 by the gap maintaining units 113 and114. Even if the light guiding plate 120 expands, the gap G1 between thepoint light source 111 and the light guiding plate 120 provided in anexpansion direction of the light guiding plate 120 is maintained by thegap maintaining units 113 and 114. According to the present exemplaryembodiment, the gap maintaining units 113 and 114 and the light guidingplate 120 face each other, but are not connected to each other.

The elastic member 160 is provided between the light source unit 110 andthe accommodation member 150, and has opposite ends fixed to the lightsource unit 110 and the accommodation member 150, respectively. Theelastic member 160 elastically biases the light source unit 110 towardthe light guiding plate 120, and its length changes depending onexpansion or contraction of the light guiding plate 120 to support thelight source unit 110. If the light guiding plate 120 expands andapplies a pressure to the light source unit 110, the elastic member 160contracts. If the light guiding plate 120 contracts, the elastic member160 expands and supports the light source unit 110. As shown in FIG. 1A,if a length of the elastic member 160 is d1, the gap between the pointlight source 111 and the light guiding plate 120 is maintained as thegap G1 by the gap maintaining units 113 and 114. If the light guidingplate 120 expands to the light source unit 110 due to heat and/ormoisture and increases in length to X, the elastic member 160 contractsand is reduced to a length d2 shorter than the length d1 as in FIG. 1B,i.e., d2=d1−X. Even if the light guiding plate 120 deforms, the gapbetween the point light source 111 and the light guiding plate 120 ismaintained. On the contrary, if the light guiding plate 120 contractsfrom the state as in FIG. 1B, the elastic member 160 increases in lengthto appropriately support the light source unit 110 between theaccommodation member 150 and the light guiding plate 120.

FIG. 3 is a sectional view of a related art backlight unit. As showntherein, a point light source 10 is fixed to an internal part of anaccommodation member 150. A gap between the point light source 10 andthe light guiding plate 120 is G2 currently, but the gap may change dueto contraction or expansion of the light guiding plate 120. That is, thegap between the point light source 10 and the light guiding plate 120may change in response to deformation of the light guiding plate 120.This means brightness of light changes. If the light guiding plate 120expands and contacts the point light source 10, the deformation of thelight guiding plate 120 and non-uniform brightness due to heat of thepoint light source 10 may occur.

According to the present exemplary embodiment, the gap between the pointlight source 111 and the light guiding plate 120 is maintained, andbrightness of light emitted to the light guiding plate 120 from thepoint light source 111 is maintained. In line with deformation of thelight guiding plate 120, the light source unit 110 may be supported tomove in accordance with the deformation.

The elastic member 160 according to the present exemplary embodimentincludes a coil spring. The material and configuration of the elasticmember 160 is not limited to the coil spring, and may include a rubberor a sponge as long as it is provided between the light source unit 110and the accommodation member 150 and elastically biases the light sourceunit 110. The elastic member 160 may plurally be provided, and should beheat resistant to maintain elasticity with respect to heat of the pointlight source 111.

According to another exemplary embodiment, the light source may includea line light source such as a lamp or a surface light source instead ofthe point light source.

According to another exemplary embodiment, gap maintaining units 113 and114 integrally formed with the point light source substrate 112 mayinclude a clamp to be coupled with the light guiding plate 120.

According to another exemplary embodiment, the backlight unit may be adirect type instead of the edge type. In this case, the backlight unitincludes a light guiding plate and a light source unit that is providedin a rear side of the light guiding plate. The backlight unit mayfurther include a gap maintaining unit formed between the light guidingplate and the light source unit, and an elastic member provided betweenthe light source unit and a lower chassis.

FIG. 4 is a perspective view of a display apparatus according to anexemplary embodiment, and FIG. 5 is a control block diagram of thedisplay apparatus.

As shown therein, the display apparatus includes a display panel 200,and a backlight unit 100 placed under the display panel 200 and emittinglight toward the display panel 200, and further includes a videoreceiver 300 and a signal processor 400.

Referring to FIG. 4, the accommodation member 150 accommodates thereflection plate 140, and the light source unit 110, the light guidingplate 120, the optical sheet 130, and the accommodation member 150 arespaced apart from each other. As shown therein, the light guiding plate120 is arranged between two point light sources 111, and light emittedfrom the point light sources 111 is incident to a lateral side of thelight guiding plate 120. The elastic member 160 provided between thepoint light source substrate 112 and the accommodating member 150elastically biases the light source unit 110 toward the light guidingplate 120. Alternatively, the point light source 111 and the point lightsource substrate 112 may be arranged along a long lateral side of thelight guiding plate 120. Further, the point light source 111 and thepoint light source substrate 112 may be arranged along the long lateralside of the light guiding plate in addition to the currently shownconfigurations.

The display panel 200 in this embodiment includes an LCD panel. Thedisplay panel 200 displays an image by adjusting molecular arrays in anLCD layer (not shown) sandwiched between two substrates. The displaypanel 200 employs light emitted from the backlight unit 100 to displayan image on a display area. The display panel 200 includes a paneldriver 210 to receive and display a video signal. A signal processingblock for providing a video signal to the panel driver 210, togetherwith a power block, is embedded on a board (not shown) and accommodatedin the accommodation member 150.

The video receiver 300 of FIG. 5 receives a video signal to be displayedas an image on the display panel 200. If a television is used as thedisplay apparatus, the video receiver 300 may receive a radio frequency(RF) signal wirelessly from a broadcasting station (not shown), orreceive a video signal based on standards such as composite video,component video, super video, Scart, high definition multimediainterface (HDMI), etc. Also, if a monitor for a computer is used as thedisplay apparatus, the video receiver 300 may receive a video signalbased on standards such as DVI, HDMI, D-Sub for transmitting RGB signalsof a VGA format, etc.

The signal processor 400 applies various preset processes to a videosignal transmitted from the video receiver 300. Here, the types ofprocesses performed in the signal processor 400 are not limited to acertain process. For example, the signal processes may include decoding,encoding, deinterlacing, frame rate conversion, scaling, noise reductionfor improving image quality, detail enhancement, etc. The signalprocessor 400 may be achieved by configurations for individuallyperforming the respective processes, or may be achieved by a singleconfiguration where various functions are integrated.

When the backlight unit 100 performs local dimming, the signal processor400 may generate a control signal for the local dimming and outputs itto the backlight unit 100. In this case, the backlight unit 100 mayinclude a light source driver (not shown), and a light source controllerto control the light source driver by receiving the control signal.

FIG. 6 is a sectional view of a backlight unit according to anotherexemplary embodiment.

In this embodiment, the backlight unit may include a graphite sheet 161as an elastic member. The graphite sheet 161 may have a thickness ofabout 1 mm˜3 mm. Graphite is a crystalline form of carbon dimorphouswith diamond, which is an electrically conductive and thermallyconductive material. The graphite sheet 161 is a natural graphiteproduct refined without additives, which has graphite's own propertiessuch as heat resistance, chemical resistance, etc., is excellent inflexibility, compression resilience, i.e., elasticity, and is availableto high temperature. Alternatively, the backlight unit may include agraphite tape instead of the graphite sheet 161. In this case, thegraphite tape may be cut from the graphite sheet in a certain width andwrinkled on a surface thereof.

FIG. 7 is a sectional view of a backlight unit according to stillanother exemplary embodiment.

In this embodiment, a gap maintaining unit 115 is placed on the pointlight source 111, and extended from the point light source substrate 112toward the light guiding plate 120. Here, the point light sourcesubstrate 112 and the gap maintaining unit 115 have an L-shaped (

-shaped section), but not limited thereto. Alternatively, the pointlight source substrate 112 and the gap maintaining unit 115 may not havethe U-shaped (

-shaped) section as long as it can maintain a gap between the pointlight source 111 and the light guiding plate 120. Thus, the gapmaintaining unit 115 may be placed under the point light source 111 andextended from the point light source substrate 112 toward the lightguiding plate 120. In this case, the point light source substrate 112and the gap maintaining unit 115 have an L-shaped (

-shaped) section.

FIG. 8 shows a light source included in the backlight unit according toyet another exemplary embodiment. The light source unit 110 in thisembodiment includes a gap maintaining unit 116 protruding between thepoint light sources 111 toward the light guiding plate 120. That is, thegap maintaining unit 116 is extended not from an edge of the point lightsource substrate 112 but from the surface of the point light sourcesubstrate 112 toward the light guiding plate 120. in this case, thepoint light source substrate 112 and the gap maintaining unit 116 mayhave a ├-shaped section. The gap maintaining unit 116 may be arrangedbetween every two point light sources 111 as shown in FIG. 8, but notlimited thereto. Alternatively, the gap maintaining unit 116 may bearranged between every several point light sources 111. Further, the gapmaintaining unit 116 may be shaped like a cylinder or a polygonalpillar.

According to another exemplary embodiment, the point light sourcesubstrate 112 and the gap maintaining unit 116 may have at least one ofa U-shape, an L-shape and a ├-shape.

As described above, according to the exemplary embodiments, there areprovided a backlight unit capable of maintaining the brightness of alight source irrespective of deformation of a light guiding plate, and adisplay apparatus including the same.

Also, according to the exemplary embodiments, there are provided abacklight unit capable of maintaining a gap between a light source unitand a light guiding plate, and a display apparatus including the same.

Although a few exemplary embodiments have been shown and described, itwill be appreciated by those skilled in the art that changes may be madein these exemplary embodiments without departing from the principles andspirit of the invention, the scope of which is defined in the appendedclaims and their equivalents.

What is claimed is:
 1. A backlight unit comprising: a light source unitwhich comprises at least one light source which emits light, and a gapmaintaining unit; a light guiding plate which guides the light emittedfrom the at least one light source; and an elastic member whichelastically biases the light source unit toward the light guiding plateso that the gap maintaining unit maintains a gap between the at leastone light source and the light guiding plate.
 2. The backlight unitaccording to claim 1, wherein the light source unit further comprises apoint light source and a point light source substrate on which the pointlight source is disposed, and the gap maintaining unit extends from thepoint light source substrate to the light guiding plate.
 3. Thebacklight unit according to claim 2, wherein the gap maintaining unit isintegrally formed with the point light source substrate.
 4. Thebacklight unit according to claim 3, wherein a section of the pointlight source substrate and the gap maintaining unit has at least one ofa U-shape, an L-shape and a ├-shape.
 5. The backlight unit according toclaim 4, further comprising an accommodation member which accommodatesthe light source unit and the light guiding plate, wherein the elasticmember is coupled to and disposed between the accommodation member andthe light source unit.
 6. The backlight unit according to claim 1,wherein the elastic member comprises at least one of a coil spring, arubber, a graphite tape, a graphite sheet and a sponge.
 7. The backlightunit according to claim 1, wherein the at least one light source isarranged along a lateral side of the light guiding plate.
 8. Thebacklight unit according to claim 1, wherein the at least one lightsource comprises a light emitting diode.
 9. The backlight unit accordingto claim 1, wherein the gap maintaining unit is configured to releasablycontact the light guiding plate in an unfixed manner.
 10. A displayapparatus comprising a video receiver which receives a video signal; asignal processor which processes the received video signal; a displaypanel which displays an image based on the processed video signal; and abacklight unit which provides light to the display panel, the backlightunit comprising: a light source unit which emits light, and a gapmaintaining unit; a light guiding plate which guides the light emittedfrom the light source unit; and an elastic member which elasticallybiases the light source unit toward the light guiding plate so that thegap maintaining unit maintains a gap between the light source unit andthe light guiding plate.
 11. The display apparatus according to claim10, wherein the light source unit further comprises a point light sourceand a point light source substrate on which the point light source isdisposed, and the gap maintaining unit extends from the point lightsource substrate to the light guiding plate.
 12. The display apparatusaccording to claim 11, wherein the gap maintaining unit is integrallyformed with the point light source substrate.
 13. The display apparatusaccording to claim 11, wherein a section of the point light sourcesubstrate and the gap maintaining unit has at least one of a U-shape, anL-shape and a ├-shape.
 14. The display apparatus according to claim 10,further comprising an accommodation member which accommodates the lightsource unit and the light guiding plate, wherein the elastic member iscoupled to and disposed between the accommodation member and the lightsource unit.
 15. The display apparatus according to claim 10, whereinthe elastic member comprises at least one of a coil spring, a rubber, agraphite tape, a graphite sheet and a sponge.
 16. The display apparatusaccording to claim 10, wherein the light source unit is arranged along alateral side of the light guiding plate.
 17. The display apparatusaccording to claim 10, wherein the light source unit comprises a lightemitting diode.
 18. The display apparatus according to claim 10, whereinthe gap maintaining unit is configured to releasably contact the lightguiding plate in an unfixed manner.
 19. A backlight unit comprising: asubstrate; at least one light source which is disposed on the substrateand emits light; a light guiding plate which guides the light emittedfrom the at least one light source; at least one gap maintaining unitwhich extends from the substrate toward the light guiding plate and pastthe at least one light source; and an elastic member which elasticallybiases the substrate toward the light guiding plate so that the gapmaintaining unit maintains contact with the light guiding plate.
 20. Thebacklight unit according to claim 19, wherein the gap maintaining unitseparates the at least one light source from the light guiding plate bya predetermined distance that is maintained by the elastic member. 21.The backlight unit according to claim 20, wherein the light guidingplate is made of material that expands or contracts with changes intemperature.
 22. The backlight unit according to claim 21, wherein theelastic member comprises at least one of a coil spring, a rubber, agraphite tape, a graphite sheet and a sponge.
 23. The backlight unitaccording to claim 19, wherein the gap maintaining unit is configured toreleasably contact the light guiding plate in an unfixed manner.